1. Field of the Invention
The present invention relates generally to a broadband wireless communication system. More particularly, the present invention relates to an apparatus and a method for supporting a synchronous Hybrid Automatic Repeat reQuest (HARQ) technique in a broadband wireless communication system.
2. Description of the Related Art
Currently, there is active research regarding the providing of services having various Qualities of Service (QoS). More specifically, there is research for providing users with services having a transmission speed of about 100 Mbps in a 4th Generation (4G) communication system. Particularly, active research is being conducted regarding the supporting of a high speed service in the form of guaranteeing mobility and QoS to a Broadband Wireless Access (BWA) communication system such as a wireless local area network system and a wireless metropolitan area network system. An example of a representative BWA communication system includes an Institute of Electrical and Electronics Engineers (IEEE) 802.16 system. The IEEE 802.16 system is a communication system which applies an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme in order to support a broadband transmission network in a physical channel.
A broadband wireless communication system such as the IEEE 802.16 system uses a Hybrid Automatic Repeat reQuest (HARQ) technique properly combining a Forward Error Correction (FEC) technique and an Automatic Repeat reQuest (ARQ) technique in order to increase reliability of data transmission. The HARQ scheme attempts error correction of initially received data, and then determines whether to retransmit data using a simple error detection code such as a Cyclic Redundancy Check (CRC). Here, the HARQ scheme is classified into a synchronous HARQ scheme and an asynchronous HARQ scheme depending on the method of determining a resource used for initial transmission, a reply to whether an error occurs, and retransmission.
The asynchronous HARQ scheme does not fix resources used for initial transmission, a reply to whether an error occurs, and retransmission. That is, in the case where the asynchronous HARQ scheme is used, a base station should separately allocate a resource for initial transmission, a resource for a reply to whether an error occurs, and a resource for retransmission. In contrast, in the synchronous HARQ scheme, resources used for initial transmission, a reply to whether an error occurs, and retransmission are fixed by resources used for the initial transmission. That is, in the case where the synchronous HARQ scheme is used, a base station allocates only a resource for initial transmission, and does not additionally allocate resources for a reply to whether an error occurs, and retransmission. Therefore, in the case where the asynchronous HARQ scheme is used, a base station should inform a terminal of resource allocation information during retransmission. In contrast, in the case where the synchronous HARQ scheme is used, a base station does not need to inform a terminal of resource allocation information for retransmission and a reply to whether an error occurs.
In a system using a synchronous HARQ scheme, there may be a case of having to allocate a resource for a system of a different standard. For example, there may be a case where an advanced system accommodates a previous system in order to guarantee a backward compatibility. At this point, when a resource allocated to a system of a different standard is not fixed, an obstacle is generated in applying a synchronous HARQ scheme. In other words, when a base station selectively allocates some resources inside a frame to a system of a different standard depending on existence of a terminal of the system of the different standard, an obstacle is generated in applying the synchronous HARQ scheme. For example, in the case where, after initial transmission is performed, a resource for a system of a different standard is allocated to the same position of the next frame as the position of a resource of the initial transmission, a resource for retransmission and the resource for the system of the different standard collide with each other.
As described above, in the case where a system using a synchronous HARQ scheme supports a system of a different standard, a resource for retransmission or a reply to whether an error occurs may not be used. Therefore, there is a need to address an obstacle caused by resource collision in using the synchronous HARQ scheme.